Okay I’m gonna give my two cents and then call it a day.
Everyone with existing resort reservations will be grandfathered in to the New Reservation System. Based on capacity, they will then allow off-site guests & non-resort AP guests to make park reservations until capacity is met. If you’re a resort guest, Disney will look at your park ticket option (park hopper vs not), or AP status to decide which parks to give you a New Reservation System reservation. They will look to see where your dining reservations or fastpasses are booked, and you will be allowed admittance into that park. If you have no fastpasses or dining, you will need to indicated in the New Reservation System what parks you want to go to that day. Park Hoppers & AP guests will have admittance to all 4 parks automatically, or Disney will dynamically choose based on your FPs and ADRs. Resort guests will need to have their choices in 8+ days in advance, and then on day 7 it will open to the public to choose (similar to Shanghai’s rolling reservation system).
Some resorts may be closed, but guests with existing hotel reservations will be moved and put into hotels that are open. I do not see Disney cancelling existing reservations if parks & resorts are open.